Limitations: Wristband isn't actually attached to sensor; no way to alter alarm once it's started.

Bottom Line: Not the most advanced technology out there, but a very convenient, user-friendly sleep aid and silent alarm.

A Closer Look at the Lark

Every human being alive wants a good night's sleep, and given that it should (if done right) occupy a third of our entire lives, the business of getting a good night's sleep ought to be one of the largest on the planet.

Which it why it's a surprise that the launch late last month of the Lark system for the iPhone ($129), a wristband and app combo that tracks your sleep, hasn't made a bigger splash. It is, in short, the easiest system ever created to help you get a good night's sleep. As an added bonus, it uses vibration rather than noise to rouse you, so it won't wake up your significant other.

Prior to the Lark, the best sleep system I'd seen was the Zeo alarm clock ($200). The Zeo asks you to wear a slim-fitting headband with a lightweight chunk of brain-reading circuitry in one end. What you get in return is total access to your sleeping brain. Throughout the night, using transmissions from the headband, the alarm clock tracks which one of four sleep states you're in, from deep sleep (the kind that makes you feel like a million dollars) to REM sleep (the bit that's interesting if you're into lucid dreaming.) In the morning you get something called a ZQ — a "sleep score" out of 100, basically — which you can try to improve on night after night.

But the troubles with Zeo are many. The ZQ would only really be interesting if we all started using it, and could therefore trash-talk each other's ZQs in some kind of massively multiplayer sleep improvement game. That is what the company was aiming for; it hasn't happened yet. The alarm clock featured an interesting graph of your night as it was unfolding, but lacked the one thing that could let you live with such a thing in your bedroom — a dimmer button. (Ironically, Zeo's literature advises you to kill extraneous light sources for better sleep.) Also, you try strapping on a headband at bedtime every night.

The Lark delivers on Zeo's promise — in a manner that is somewhat less informational but way more user-friendly. This time, it's a wristband rather than a headband. It feels like putting a watch on when you go to bed. But the plastic velcro-wrapped doohickey, which recharges on a tiny nightstand, is transmitting to your iPhone the whole time. The Lark app runs in the background on the iPhone, so your phone can be off the whole night. (Always a good idea to keep an iPhone plugged in when it's running an app for seven or eight hours, of course.)

So what do you get in the morning? Well, the Lark can't read your brain. It can't tell you when you're in REM sleep or deep sleep, which is a pity. But once you've strapped it on, the Lark is like Santa Claus — it sees you when you're sleeping and knows if you're awake.

How? Because the wristband is incredibly sensitive to tiny movements. It turns out that when we sleep, we're as good as paralyzed. All those rolling over tricks we do at night are actually brief moments of wakefulness. And if you're awake, you're moving, if only slightly. Go ahead, try to keep your wrist perfectly still for more than a minute. Try pretending to be asleep. The Lark knows all.

In the morning, you'll know how long it took you to fall asleep (a very good indicator of your sleep health), how many times you woke up in the night and how many hours and minutes you slept for, cumulatively. For $60 more, you can get access to a "personal sleep coach" via the Lark website, as well as a Myers-Briggs-style assessment of your "sleep type." But I'm not sure that extra cash is entirely necessary here. Simply seeing a string of four, five or six-hour nights in the "sleep history" tab on the Lark app, alongside the admonition that "you slept too little," is enough to shame you into doing all the stuff sleep experts tell us to do: head to bed earlier, banish light sources and TVs from the bedroom, and don't drink in the few hours before bed.

The Lark isn't perfect, of course, being a first generation device. There is no way to change an alarm once you've set it, and there are too few instructions included in the box. The velcro wrist strap simply wraps around the sensor, which means the two can get easily separated when plugging it in to the rechargeable dock. And would it have been so hard to include an iPhone charger in the dock itself, rather than making you plug a charger cable into the back?

But none of these caveats are worth avoiding the Lark for, if you're interested in learning how you sleep and learning to sleep better. The vibrating alarm worked every time for me, and I'm often harder to wake than a bear in January. If you're worried, though, there is a backup alarm sound available on the app under the "peace of mind" setting. A few weeks with this device and the hope is that you'll have plenty of that.

Want to sleep like a baby? Lark can help

Meet Lark

The sleep aid product is lovingly presented, even if the cover model does look a little too much like Tom Cruise.

In The Dock

The transmitter plugs into its own charger. The poor old iPhone only gets a furrow to lie in. If you want to charge it, you have to plug the iPhone cable into the back of the dock.

The Charger

A close up of the dock you'll have to keep on your nightstand.

The Transmitter

Here's what it looks like wrapped around your wrist with a velcro strap. If you're a guy, watch out for trapped hairs.

On the Screen

Here's the kind of information you get in the morning: how long you slept for, how many times you woke up (the graph shows how long for), and a sleep score out of 10.

Nudge, Nudge

Someone at Lark is a fan of Monty Python.

Series Supported by Energizer®

The Gadget of the Day Series is supported by the Energizer® Inductive Charger, which brings you the next generation of charging with Qi technology. Qi is the new universal standard for wireless charging. Energizer® has always been designed with performance and responsibility in mind ... now that’s positivenergy™.

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